The present invention relates to a rolling mill, a rolling method and a rolling mill system for metal strips, and more particularly to a rolling mill with upper and lower rolls and/or upper and lower back-up rolls arranged in crossed relation to each other, a rolling method using such a rolling mill, as well as a rolling mill system including such rolling mills.
As one of strip crown control methods for metal strips, particularly, in hot rolling, there has recently been adopted a scheme of arranging rolls to cross each other. For a 4-high rolling mill, as disclosed in JP, A, 47-27159, the pair cross type that work rolls and back-up rolls are both crossed each other has been practiced for the purpose of avoiding an excessive axial thrust force acting on the work rolls. In this prior art, because the center of a chock for the back-up roll which bears the rolling load is deviated from the center of a screwdown screw or a hydraulic cylinder which serve as a screwdown device, the chock is subjected to twist moment, which causes local load on a sliding face between the chock and a mill housing. Therefore, smoothness of the screwdown operation is diminished and wear of the sliding face is accelerated. To prevent such drawbacks, it has been proposed to balance moment between the drive side and the operation side by, for example, providing an equalizer beam of large rigidity as disclosed in JP, A, 56-131004 and JP, A, 56-131005, or providing a thrust beam as disclosed in JP, A, 57-4307.
It is also known from the description of JP, A, 60-83703, for example, that since the cross arrangement of work rolls causes a metal strip to be deformed in a direction perpendicular to the rolling direction as well, metallurgic quality of the metal strip is improved in some cases.
Meanwhile, a roll cross mill which requires no equalizer beam of large rigidity has been attempted by making only work rolls crossed, other than back-up rolls. This attempt was proposed earlier than the pair cross mill as disclosed in JP, A, 47-27159, for example, but has not succeeded in practical application up to date.